1. Technical Field
The present invention relates to an electro-optical substrate, a method for designing the same, an electro-optical device, and an electronic apparatus.
2. Related Art
Liquid crystal panels used as electro-optical devices in electronic apparatus such as projectors receive light entering from one of the surfaces of the liquid crystal panel, and spatially modulate this light. Patterns such as images and characters are formed by emitting the specially modulated light from the other surface of the liquid crystal panel. Here, a structure is used, the light-shielding layer therein between the light source of this light and thin film transistors being used in order to suppress the generation of a photo leakage current originated by the light penetrating the channel regions of the thin film transistors that drive the liquid crystal panels.
There are cases, in which the light entering from one of the surfaces of the liquid crystal panel breaks off to stray light by the reflection from the other surface of the liquid crystal panel, and this stray light penetrates the semiconductor layer of the thin film transistor. A structure used in order to prevent such stray light from penetrating the thin film transistor includes a shielding layer provided between the thin film transistor and the electro-optical substrate. This light shielding layer prevents the stray light from directly penetrating the semiconductor layer of the thin film transistor.
In recent years, applying a silicon-on-insulator (SOI) technique has been examined as it becomes necessary for the write-in time per pixel to grow shorter and the image contrast to improve. Using the SOI technique allows replacing the polycrystalline thin film transistors with single crystalline thin film transistors that have high mobility, thereby providing high speed switching. JP-A-10-293320 describes a method for obtaining a light-shielding layer close to a substrate using the SOI technique. The manufacturing method includes: the forming of a light-shielding layer on an optically transparent substrate surface; covering the surface with a silicon oxide layer and planarizing it with polishing; bonding a single crystalline silicon substrate on the planer surface; and removing the single crystalline silicon substrate, leaving the thin layer of the single crystalline silicon, so as to form an SOI substrate.
Random-reflecting light is present in the interior of a display device provided with a liquid crystal panel, due to the multiple optical parts and components of the display device. Except for the light entering vertically to an electro-optical substrate in which thin film transistors are formed, the intensity of light obliquely penetrating the electro-optical substrate as the stray light is increasing. In recent years in particular, the brightness of the light source is increasing in order to obtain brighter images, and thus the stray light intensity penetrating the thin film transistor also tends to increase. In order to avoid the decline in the image display quality resulting from the generation of photo leakage currents generated by the stray light, an electro-optical substrate with a sufficient light-shielding property against the obliquely penetrating stray light is necessary.
If a single crystalline silicon layer with a high crystalline property (for instance, an SOI structure) is used as a semiconductor composing the thin film transistors, there is almost no recombination of carriers such as electrons and holes generated by the excitation caused by the penetration of stray light. Therefore, in order to reduce the generation of photo leakage currents caused by the penetration of stray light, the photo leakage currents passing through a source and a drain of a semiconductor device, a higher level of light-shielding property is required compared to the case where a polycrystalline silicon layer is used. According to the research of the inventor, there is a problem that in the case of using a single crystalline silicon layer, compared to the case of using a polycrystalline silicon layer with a larger amount of crystalline defects, the amount of the photo leakage current is increased by a factor of ten, resulting in a decline in the display image quality.